The present invention relates to fluorescent cobalamins (sometimes referred to herein as CobalaFluors) and uses of these compounds. More particularly, this invention relates to fluorescent cobalamins comprised of a fluorescent, phosphorescent, luminescent or light-producing compound that is covalently linked to cobalamin. These fluorescent cobalamins can be used as diagnostic and prognostic markers (a) to distinguish cancer cells and tissues from healthy cells and tissues, including identifying lymph nodes containing cancer cells, and (b) to determine if an individual will respond positively to chemotherapy using cobalamin-based therapeutic bioconjugates.
The publications and other materials used herein to illuminate the background of the invention, and in particular cases, to provide additional details respecting the practice, are incorporated by reference, and for convenience are referenced in the following text by author and date and are listed alphabetically by author in the appended bibliography.
Rapidly-dividing cells require cobalamin as a cofactor for the enzyme methionine synthase to support one-carbon metabolism prior to DNA replication (Hogenkamp et al., 1999). In acute promyelocytic leukemia, a 3-26 fold increase in the unsaturated B12 binding capacity of blood is observed, due to an increase in the concentration of the B12 binding proteins transcobalamin and haptocorrin (Schneider, et al., 1987; Rachimelwitz, et al., 1971). Some patients with solid tumors also exhibit a significant increase in the circulating levels of transcobalamin and haptocorrin (Carmel, et al., 1975). The increase in unsaturated serum cobalamin binding capacity corresponds to the increased uptake of cobalamin by rapidly dividing cells. Tumors even sequester sufficient cobalamin for diagnostic imaging purposes if a gamma-emitting radionuclide, such as 111In, is attached to cobalamin through the octadentate chelator diethylenetriaminepentaacetic acid (DTPA) (Hogenkamp and Collins, 1997). This has been demonstrated in mice with an implanted fibrosarcoma (Hogenkamp and Collins, 1997), as well as in humans with breast cancer (Collinset al., 1999), and in tumors of the prostate, lung, and brain (Collins et al., 2000).
In the sentinel lymph node concept for melanoma and breast cancer surgery, a dye or radionuclide is injected into the tissue around the tumor to identify the first lymph node that drains the tumor (Morton et al., 1992; McGreevy, 1998). This node is termed the sentinel node, and it is removed for diagnostic tests to determine the extent of metastasis beyond the primary tumor. This procedure is controversial, as it fails to detect metastatic disease in about 12% of patients (McMasters et al., 1999). The dye or radionuclide that is injected is not specific for cancer cells, but merely identifies for the surgeon the primary lymph node that drains the region of the tumor. The high false-negative rate should be improved dramatically by using a fluorescent marker that is specific for cancer cells.
Thus, there exists a need for an agent that can be used for the diagnosis and prognosis of cancer tissue or cells with improved results.